(1) Field of the Invention
The present invention relates to the construction of an electronic document filing system having a document retrieving function for sequentially displaying electronic documents filed in a database page by page, or a so-called page-turning retrieval function, and to a method thereof.
(2) Description of the Related Art
As word processors and Desk Top Publishing (DTP) systems have become popular, not only preparing a document in the form of electronic data, but also storing the electronic document into a database has become common. Given these circumstances, research on techniques that facilitate retrieving a desired document from the database have been actively performed.
The electronic document filing system disclosed, for example, in U.S. Pat. No. 4,931,984 or U.S. Pat. No. 5,047,868 is known as an electronic document filing system that stores an electronic document to display it for retrieval in a later time.
FIG. 1 is a block diagram depicting the construction of a conventional electronic document filing system. The electronic filing system comprises a controller 121, a CRT display unit 122, an image reader 123, an optical disk deck 124, a hard disk unit 125, a printer 126, an automatic document transporter unit 127, and a keyboard 128. The CRT display unit 122, image reader 123, and controller 121 are connected by image buses, while the optical disk deck 124, hard disk unit 125, printer 126, and controller 121 are connected by the image buses and command buses. Further, the automatic document transporter unit 127, keyboard 128, and controller 121 are connected by the command buses.
The conventional electronic document filing system constructed as above operates the following way.
First, the operation for filing a document with the electronic document filing system will be explained. Once a document is set on the automatic document transporter unit 127, the automatic document transporter unit 127 automatically transports the document onto a scanner of the image reader 123. Then, the image reader 123 reads the document to convert it into image data, and outputs the document image data to the controller 121. The controller 121 stores the document image data into the optical disk deck 124 upon the receipt thereof. Simultaneously, the controller 121 stores two other data into the optical disk deck 124: a key word corresponding to the document that a user has entered with the keyboard 128 and retrieval-use-image data produced by applying a pixel skipping method to the document image data so as to match the resolution thereof with the CRT display unit 122. The location of these data in the optical disk deck 124 are stored into the hard disk unit 125.
Next, the operation for retrieving a desired document from the filed documents will be explained. To begin with, the user enters the key word for retrieval with the keyboard 128. Accordingly, document data corresponding to the key word are extracted from the optical disk deck 124. Subsequently, so-called page-turning retrieval is performed, whereby the user can find a desired document or page from the extracted document data. In other words, the extracted document data are sequentially displayed page by page on the screen of the CRT display unit 122 as if the user was turning the pages of a book. Note that the document data displayed on the screen are the retrieval-use-image data produced through the pixel skipping method at the time of document filing. The operator changes the displays on the screen sequentially as he watches the images of the retrieval-use-image data until he finds the desired document or page. The data related to the document found in this way are outputted to the printer 126 in accordance with a command entered with the keyboard 128. Note that the data outputted to the printer are not the retrieval-use-image data, but the document image data initially produced by the image reader 123.
However, with the conventional electronic document filing system, it is necessary to produce the retrieval-use-image data prior to the page-turning retrieval, which necessitates an extra memory area for storage. Although the pixel skipping method is applied, the amount of the resulting data, or namely the retrieval-use-image data, is still massive; for the amount of the original image data is monumental. Given that a massive amount of data are processed in the extra memory, it takes quite long to display the retrieval-use-image data, which resulting in a problem of decreasing the overall retrieval speed.
There is another example of a conventional electronic document filing system, wherein data in a specific area within a document are retrieved and thence displayed sequentially. With this type of system, only electronic documents in a standard format are subject to the retrieval. Thus, the user specifies an area found in every page of the document such as a name column with the input unit. Accordingly, the system extracts the image data corresponding to the specified area among the stored document image data to sequentially display the corresponding image data alone. In this way, the page-turning retrieval is performed at a high speed.
However, the electronic document filing system described as above invariably displays the image data in the specified area whether there exists image data in the area or not; a blank is displayed when no image data exists. Although the blank display does not happen frequently when retrieving documents in the standard format, a blank or image data in a non-specified area may be displayed when retrieving documents in a variety of non-standard formats. When this happens, the time spent for retrieval turns to be a waste, causing the system to decrease the retrieval operation speed.